Ultrasonic welding is the process of fusing two work pieces together using ultrasonic acoustic vibrations. Ultrasonic welding can be used for both hard and soft plastics, such as semicrystalline plastics, and metals. Typically, the materials are sandwiched between a welding tip, also referred to as a sonotrode or horn, and an anvil. The welding tip imparts the ultrasonic vibrations to the work pieces, which locally melts or transforms the work pieces around the point of contact. This local material transformation is a result of the work pieces absorbing the vibration energy. The joint may be formed by either by fusion or covalent bonds in the case of dissimilar metals as a result of the input energy which includes the frequency and amplitude of the vibrations, the surface properties of the joining materials, and the pressure applied at the intended joint.